Extendible interlocked boom



Jan. 2, 1968 J, R. SHARMAN ET AL 3,360,894

EXTENDIBLE INTERLOCKED BOOM Filed June 20, 1966 2 Sheets-Shet 1 INVENTORS JOHN R. S'HARMAN 8 MAX A.ORR

YMg k ATTORNEYS 1 Jan. 2, 1968 R H R ET AL 3,360,894

EXTENDIBLE INTERLOCI'ZED BOOM 2 Sheets-Sheet 2 Filed June 20, 1966 JOHN RJSHARMAN MAX A. ORR 8117M PM ATTORNEYS United States Patent 3,360,894 EXTENDIBLE INTERLOCKED BOOM John R. Sherman, Silver Spring, Md., and Max A. Orr, Falls Church, Va., assignors to Melpar, Ind, Falls Church, Va., a corporation of Delaware Filed June 20, 1966, Ser. No. 558,741 4 Claims. (Cl. 52-108) The present invention relates generally to strip-like units which may be rendered reversibly flexible and rigid, and more particularly to a flexible strip which is extendible to form a tubular boom of high torsional rigidity.

It is well known that a properly prestressed elongate strip of resilient material may be coiled in a flattened open condition on a reel or drum, when uncoiled, will assume a tubular or semi-tubular shape of greater structural rigidity. Generally, the prior art proposals for extendible booms or coilable tubes have required that the strips from which the final tubular structures are formed be specially preformed or prestressed, by way of conventional treatment, such that when the strip is unrestrained, assumption of the tubular shape is assured. When the strip is to be subequently plated or coated, as is frequently the case where the boom is to be used in antenna applications, difliculty is encountered in handling the prestressed strip during the coating operation, and has led to the requirement of expensive and timeconsuming special techniques in the production process.

Moreover, use of the coilable tube as an extendible antenna boom or mast for spacecraft or more conventional mobile communications units, or in other applications such as aircraft-stored steady lines for groundto-air pickup of men or materials, and radar reflectors for survival craft (e.g., lifeboats), requires that the extended extended structure have high torsional rigidity to insure reliable deployment and maintenance of structural characteristics despite possible subjection of the device to undesirable forces tending to produce collapse or rupture. The greatest problem encountered in attempts to supply the extended boom with the necessary rigidity and stability resides in the provision of positive means for locking the longitudinal edges of the stored strip as it is deployed to form the tubular structure. In the past, the tube seam or joint has been formed by such methods as providing each of the longitudinal edges of the strip with an alternating pattern of tabs and notches adapted to mate in interlocked fashion with the notches and tabs, respectively, of the opposite edge; or providing spaced tabs on one edge of the strip and mating slots adjacent the other edge so that each tab passes through a respective slot as the prestressed strip is uncoiled, or if the strip is not preformed, bending or otherwise forcing each tab into an associated slot. None of these prior art methods provides a positive interlocked seam endowing the boom structure with high torsional rigidity and shear strength. The use of tab-notch pairs creates an additional problem of achieving desirable integrity of interlock between a large percentage of the pairs during deployment of the boom. The tab-slot arrangement depends heavily on the spring characteristics and prestressing of the strip material to achieve the necessary interlock forces. A further disadvantage of the tab-slot method using unstressed strip material is that additional mechanisms are required in the boom deployment system to bend or force the tabs into the mating slots.

Accordingly, it is a primary object of the present in- 3,360,894 Patented Jan. 2, 1968 vention to provide an extendible boom or coilable tube having an improved interlocked seam.

Briefly, according to the invention the resilient strip material is fabricated without preforming or prestressing, and the longitudinal edges thereof are provided with opposed tab and slot members, each member being inwardly folded along the strip surface which is to become the inner wall of the tube when the strip is deployed as a boom structure. These members are spaced according to the load application and operating environment in which the boom is to be used, and the diameter of the drum or reel on which the coil strip is stored. Each slotted member or slotted flap is preferably provided with a pair of slots, one in the folded portion thereof and the other in the unfolded portion in substantial registry with the first slot. A separate guide slot is provided adjacent each tab member near the edge of the strip to accept the respective folded slotted member as the boom is deployed via a tube-forming mandrel in the boom deployment system. The boom is so confined as it passes from the end of the mandrel that its diameter will increase upon relaxation of the physical constraint imposed by the mandrel with continued extension of the boom. In this manner, as the boom exits from the forming mandrel, related tab-slot members are positioned in overlying relation along the inner surface of the tube, the slot memher having entered the respective guide slot during the forming operation. Upon continued extension of the boom its diameter will increase as the strip material tends to return to its flat state, thereby forcing the inwardly folded portion of each tab into the slots of the respective slotted member and forming a positive interlocked seam. Because of the manner in which locking is accomplished in extendible booms according to the present invention, problems such as loss of interlock caused by disengagement under thermal expansion are eliminated. In addition, locking does not depend upon any prestressing or preforming of the strip material nor upon retention of spring properties. Also, since preforming is not required, the application of special coatings or platings to the boom surface is vastly simplified in that the strip material may be coated while in the free flattened state without the need for special handling techniques.

It is therefore another object of the invention to provide an extendible boom formed from resilient strip material which need not be subjected to special preforming.

A further object is to provide a tubular device of the above-stated character wherein an interlocked seam is provided by means of folded or bent-over slot and tab members spaced in mating relationship along the longitudinal edges of the strip from which the tubular structure is formed.

Still another object of the invention is to provide an interlocked seam for an extendible boom wherein positive locking is assured by an increase in boom diameter during deployment.

The above and still further objects, features and attendant advantages of the invention will become apparent from a consideration of the following detailed description of a preferred illustrative embodiment thereof, especially when taken in conjunction with the accompanying drawings, in which:

FIGURE 1(a) is a plan view of the strip material showing the manner in which the tab members and slot members are formed;

FIGURE 1(b) is an end view of the structure of FIGURE 1(a);

FIGURE 2 is a perspective view of a portion of the boom forming assembly showing the manner in which the boom is deployed;

FIGURE 3 is a perspective view of the partially formed (i.e., partially rolled) boom structure;

FIGURE 4 is a view taken along the lines 44 of FIG- UREB;

FIGURE 5 is a fragmentary perspective view of the inner portion of the boom seam as the boom leaves the forming mandrel; and

FIGURE 6 is a fragmentary perspective view similar to that of FIGURE 5 after the boom diameter has undergone an increase with continued deployment.

Referring now to the drawings, a strip, ribbon or tape 10 of suitable resilient material, such as beryllium copper,

and having a, thickness depending upon the environment in which the subsequently formed boom is to be used and the expected loading to be placed on the boom, is provided with a series of preferably equally spaced tabs 21 along one of its longitudinal edges and a like series of tabs 23, longitudinally aligned with tabs 21, along the opposite longitudinal edge. The particular shape of these tabs is immaterial to the essence of the invention so long as certain critical factors are taken into account, as will bediscussedin the ensuing description. It is to be noted, then, that the tab shapes illustrated in the several figures are to be taken as exemplary.

Also by way of example, the basic boom strip with edge-projecting tabs may be fabricated in any convenient and conventional manner, such as by punching or cutting from strip material of larger dimensions.

A series of guide slots 26 are provided in longitudinal alignment, parallel to the longitudinal edge of strip 10 from which tabs 21 project, a separate guide slot associated with each tab and positioned at a common center line therewith. Each of the tabs 23 along the opposite edge of strip 10 is provided with a pair of parallel slots 28, 29, that one of which more remote from the strip edge preferably being wider than the other, but both having dimensions sufficient to accept the end of related tab 21 with a relatively close fit.

Each of tabs 21 is folded or bent over along a fold line 30 corresponding to the longitudinal edge from which it projects, to form a folded tab member or tab flap 35. Similarly, each of tabs 23 is folded or bent over along a fold line 32, except that the latter fold line is spaced from the longitudinal strip edge so that the end of each folded tab 23, lies approximately along the strip edge. In this manner a series of slotted members or slotted fiaps 38 is formed, each of members 38 still projecting from the strip edge, while members 35 now lie almost entirely within the strip Width.

After folding, the slots 28, 29 in slotted member 38 should be positioned in substantial registry, and to this end, the longitudinal center line of each of these slots is located approximately equidistant from the desired fold line (i.e., 32) during the slot forming process. Also, the dimensions of guide slots 26 are predetermined to permit entry of the related slotted member 38 therein during the boom forming process.

Referring to FIGURE 2, the strip 10, which is coiled for storage on a drum or reel 42 of a conventional boom forming assembly or deployment system, is converted to a rigid tubular structure 48 upon passage through a cylinvder-fo'rming mandrel or guide 51 under the driving force exerted by a motor driven sprocket 53. The strip 14 may be'provided with a series of longitudinal aligned apertures (notshown) arranged to mate with the pins on the drive sprocket so that it is readily pulled, i.e., uncoiled, from the storage drum. A pressure roller 56 is provided near the end of the frusto-conical guide 51 to insure that the slotted members 38 enter the related guide slots 26.

FIGURES 3 and 4 illustrate the partially rolled strip and the positions of associated tab members and slotted member at this point of the boom forming process. The strip edge containing slotted members 38 is forced to pass outside the edge containing tab members 35, such as by use of a conventional edge separator (not shown) within guide 51.

In FIGURE 5 there is shown a tab member-slotted member combination as the boom passes from the end of guide 51 remote from storage drum 42. This end of guide 51 is provided with a diarneter sufficient to impose a restraint on the extending boom 48, such that the boom diameter is less than that which will occur with further extension beyond the guide end. Since the boom is composed of resilient material and has not been preformed, its natural tendency is to return to the open fiat state; but as will be noted from FIGURE 6, it is prevented from doing so by the position of the tab and slotted members. In the confined state shown in FIGURE 5, slotted member 33 is retained within guide slot 26 in overlying relation to associated tab member 35, i.e., between the tab member and the inner surface of the tube and with slots 28, 29 located beyond the end 69 of the tab member.

As the boom is further extended from the end of frustoconical guide 51, its diameter increases and tab member 35 is trapped by the slots of member 38 (FIGURE 6) sliding therethrough under the forces accompanying the natural expansion of the boom. In this manner, the boom is provided with a fully interlocked seam and no disengagement is possible short of complete rupture of the boom.

While we have disclosed a preferred embodiment of our invention, it will be apparent that various changes and modifications in the specific details of construction which have been illustrated and described may be resorted to without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. An extendible boom, comprising an elongate strip of resilient material having a plurality of spaced tab members formed on one of the longitudinal edges thereof and a plurality of slotted projecting members formed on the other of the longitudinal edges thereof, said slotted mem bers being positioned opposite said tab members, a plurality of longitudinal guide slots adjacent said one of said longitudinal edges and spaced in cooperative relationship with said tab members to accept said slotted members when said strip is rolled about a longitudinal axis thereof, and slots in said slotted members arranged to accept related tab members after entry into said guide slots, to form an interlocked seam for said boom.

2. The invention according to claim 1 wherein said tab members are bent over toward the longitudinal axis of said strip on a fold line corresponding to said one of said longitudinal edges, and said slotted members are bent over toward said longitudinal axis on a fold line spaced from said other of said longitudinal edges, each of said tab members and said slotted members being bent to lie adjacent the surface which is to become the inner surface of said boom.

3. The invention according to claim 2 wherein each of said slotted members has a pair of slots, arranged to fall in overlying registry when the respective slotted member is bent over, so that each of said tab members is engaged by said pair of slots on the related slotted member.

4. An extendible boom system comprising the strip according to claim 1; means for storing said strip in a flat coiled condition; means for withdrawing said strip longitudinally from said coiled condition; means for rolling said strip about a longitudinal axis thereof in the form of a cylinder with a diameter less than the natural diameter of said boom as said strip is withdrawn from said coiled condition to cause successive entry of said slotted members into said guide slots, whereby the slots in said slotted 5 members engage the related tab members as said boom 3,177,987 4/1965 Swaim 52108 is extended to assume its natural diameter. 3,193,432 7 5 Baines 5 References Cited FOREIGN PATENTS UNITED STATES PATENTS 5 429,609 5/1926 Germany. 1,028,829 6/1912 Reuterdahl 29 513 XR 1,534,990 4/1925 Pritchard 138166 FRANK ABBOTT Prlmary Exammer- 3,144,104 8/1964 Weir et a1 52108 PRICE C. FAW, Assistant Examiner. 

1. AN EXTENDIBLE BOOM, COMPRISING AN ELONGATE STRIP OF RESILIENT MATERIAL HAVING A PLURALITY OF SPACED TAB MEMBERS FORMED ON ONE OF THE LONGITUDINAL EDGES THEREOF AND A PLURALITY OF SLOTTED PROJECTING MEMBERS FORMED ON THE OTHER OF THE LONGITUDINAL EDGES THEREOF, SAID SLOTTED MEMBERS BEING POSITIONED OPPOSITE SAID TAB MEMBERS, A PLURALITY OF LONGITUDINAL GUIDE SLOTS ADJACENT SAID ONE OF SAID LONGITUDINAL EDGES AND SPACED IN COOPERATIVE RELATIONSHIP WITH SAID TAB MEMBERS TO ACCEPT SAID SLOTTED MEMBERS WHEN SAID STRIP IS ROLLED ABOUT A LONGITUDINAL AXIS THEREOF, AND SLOTS IN SAID SLOTTED MEMBERS ARRANGED TO ACCEPT RELATED TAB MEMBERS AFTER ENTRY INTO SAID GUIDE SLOTS, TO FORM AN INTERLOCKED SEAM FOR SAID BOOM. 